All information on this page is copied material from Gulvfakta, which is a technical reference material, Source: Gulvfakta Subfloors Materials for flooring

All information on this page is copied material from Gulvfakta, which is a technical reference material, Source: Gulvfakta Subfloors
Subfloors are a common term for a continuous surface that acts as a base for the actual floor covering. The subfloor can be made up of smaller units that are assembled at the workplace (e.g. chipboards, or boards/paneled floors) or laid out at the workplace as a liquid mass which, after solidification, also forms a continuous surface (cast subfloors). Hard insulation materials, cork parquet etc., are not considered subfloors, as they do not form a surface that can be used as a work floor. Also note that a floor structure in this context is not counted as a subfloor/subfloor but as part of the load-bearing structure. Beam constructions are dealt with in the chapters Wooden floors and Subfloors made of board materials. Execution of the subfloor should, to the greatest extent possible, be included in the floor contractor's contract so that the responsibility for the execution with regard to the construction's appearance and usability is located in the same place.

It is the subfloor that is the basis for the finished floor's functional properties, e.g. with regard to:
Strength - depending on use, but basically the same as the supporting substrate.
Flatness - requirements for screeding.
Moisture - constructive structure, moisture barrier.
Sound and gait - flexibility of the constructive design of the middle layer.
Lifetime - material selection, design, use.

Important properties for subfloors
The properties of the subfloor must be matched in relation to the chosen floor covering and the building physical requirements for the entire floor construction.

The required properties are not the same for all floor substrates. In the following, some of the properties of floor substrates which can be particularly important are briefly discussed:
Carrying capacity
The subfloor must be able to transfer the loads that can be expected in future use, without unwanted deformations or damage occurring. With wooden floors, be aware that the surface of the subfloor can be exposed to significant tensile stresses as a result of the wood's moisture-dependent movements.
Strength and stiffness/elasticity
The substrate for the floor covering must be able to withstand the static and dynamic loads, e.g. from payloads, furniture, people and rolling traffic, which must normally be expected to occur in the intended use.
For reasons of walking comfort, a certain flexibility (elasticity) may be desirable, while on the other hand, excessive deformations must not occur due to normal loads during use.
The substrate for the floor covering must be so flat that the floor can achieve the desired flatness. For thin floor coverings and non-load-bearing wooden floors, this means that the substrate must be able to be laid out with the same flatness as desired by the finished floor, section Flatness and floors
Height leveling
The subfloor must be able to accommodate minor height differences in the underlying supporting structure.
Moisture barrier effect
In order to reduce the risk of damage due to moisture transport from below, e.g. due to construction moisture, it may be necessary to provide the floor substrate with a moisture barrier, see sections Moisture measurements in concrete decks and Construction moisture
Stability against moisture
The floor must not suffer harmful deformations due to moisture effects resulting from normal use.
Acoustic properties
The substrate must have such sound technical properties that it can contribute to reducing the transmission of airborne sound, footstep sound and drum sound. You can read more about this area in the sections Choosing a floor and Sound and floors
Heat resistance
Floor materials to be used in connection with underfloor heating systems must be able to withstand the temperatures that can be expected to occur in the current construction.
Heat insulating effect
The subfloor must contribute to the thermal insulation of the deck construction.
The floor substrate must retain its properties to a satisfactory extent over a long period of time exposed to normal degradation factors, e.g. moisture or physical stresses from use. Materials for flooring
A subfloor can be made up of several layers and of many (different) materials that can be laid out according to different principles, see also table 1.

Table 1: Underfloor material groups and construction principles.

Subfloors made of sheet materials and cast subfloors are dealt with in the two subsequent sections. Flooring is often attached to the subfloor by a gluing process. Glue and associated primer are also dealt with in a separate section.